A weblog for professionals in electrical, electronic, mechanical and software engineering with content provided by the members of the Long Island Consultant's Network.

June 2011

June 30, 2011

A tree is not a telephone pole, yet you so often see self proclaimed tree experts, self proclaimed "arborists" whom I can only refer to as professional screw-ups, improperly planting new trees or improperly altering the planting of existing trees by mounding soil up the tree's trunk way too high.

Just look at these photos of two unfortunate neighborhood trees on which this blunder has been inflicted:

To see what the sad consequences of making this mistake can be, please take a look at:

June 28, 2011

In the year 1924, when my mother was seventeen, she was stricken with polio which paralyzed her entire right side.

She was taken care of as well as anyone could have been at the time. Treatment consisted of receiving electrical muscle stimulation from an induction coil that was mounted on a wooden box. The stimulator's coil was mounted to the box on top of a painted wooden panel. In the center of the coil, there was a sliding brass plunger which was used to control the energy delivered to the patient during each treatment.

June 23, 2011

We saw before that for a zero to +E square pulse train, that the RMS value equals the average value divided by the square root of the duty cycle. The narrower the duty cycle gets, the higher the ratio of the RMS to the average becomes.

Here, we look instead at the ratios of RMS to average for sine tips of different conduction angles.

In each case below, the waveform goes from zero to +100 and back again to zero along sinusoidal trajectories. The RMS and average values for several conduction angles are calculated and their ratios are compared.

June 21, 2011

The Loop Current (LC) enters the Gulf of Mexico (GoM) at the Yucatan Peninsula and sometimes flows around Cuba and goes directly into the Florida Straits (FS). Then, as time progresses, the LC intrudes increasingly into the GoM and makes a right-hand U-turn to return and connect with the FS. This trombone-shaped path can extend several hundred kilometers toward New Orleans and sometimes can come uncomfortably close to New Orleans. This poses a hurricane danger to the Gulf Coast because deep warm water accumulates inside the loop and can supply energy to hurricanes that pass through the loop. We know this water is warm because radar altimeter maps of the sea surface show peak elevations 70 cm or more. These raised portions are there for periods of many months, and this requires that they contain warmer, lighter water.

June 18, 2011

To subtract one number from another, you can do the usual arithmetic algorithm, but you can also use an addition process instead that can be handy for checking subtraction results when working by hand. This avoids doing the identical process with which you got your first result lest you inadvertently repeat making an error you might have made the first time.

Consider the following examples:

8718 - 4732 = 3986 This is completely standard arithmetic.

Now, replace the "4732" with its nines complement which in this case means "5267". Each digit of this new number is that which if added to the corresponding digit of the old number, totals to nine. Ergo, 4+5=9, 7+2=9, 3+6=9 and 2+7=9.

June 14, 2011

A recent article by John Dunn (Ground - 6/9/11) brings to mind a classic story. Its most likely an urban legend, but its such a good one that it bears retelling, especially for the young folk among us who may have never heard it. It dates back to when telephones were too big to lose, and actually had wires attached to them.

The phone man was sent out on a call with the following bizarre

complaint: When the little old lady received a phone call, the caller complained that the phone had rung many times before she answered. But she knew she answered on the second ring. Interestingly enough, though, whenever the phone was about to ring, her dog barked first.

June 11, 2011

The company had hired an engineer for a microwave project and the fellow dug into the work with energy and gusto. He seemed genuinely happy, until......

The planned design was going to need some stripline structures, but an examination of several circuit boards convinced this engineer that the available geometric precision of circuit board artwork at that company was inadequate for the purpose at hand. Therefore, he brought in from home an utterly exquisite set of precision carving knives and working by hand, he actually carved the required stripline structures out of raw copperclad circuit boards without ever etching them.

His stripline carvings were wonders to behold. Engineer after engineer, upon seeing them, walked away awestruck.

June 09, 2011

There was this 12-bit analog-to-digital converter (ADC) which was set up for testing in a fixture that this fellow had assembled in a 19-inch rack that was maybe seven feet tall.

First, let's look at some numbers:

The ideal mV steps of this ADC were one part in the twelfth power of two, take away one (for zero to +5V exactly). That comes to 1/(212 - 1) or 1/4095. At the ADC's full scale voltage of five volts, that comes to a nominal resolution of 5/4095 volts which is very nearly 1.221 mV. The ADC tests were failing their test limits and I was asked to find the reason why which did not please the fellow who had set up that rack. I began the process anyway.